Methods of making triacylglycerol using phospholipid:Diacylglycerol acyltransferase

ABSTRACT

The present invention relates to the production of triacylglycerol in a transformed organism or host cell, by means of a nucleotide sequence from  S. cerevisiae,  whereby said enzyme catalyzes the transfer of fatty acids from phospholipids to diacylglycerol in any acyl-CoA-independent reaction. The transformation of the organism or host cell results in increased oil content.

The instant application claims the benefit of U.S. ProvisionalApplication 60/180,687 filed Feb. 7, 2000, 60/132,010 filed Apr. 30,1999 which is a continuation of U.S. Ser. No. 09/329,802, filed Jun. 10,1999, now abandoned and claims foreign priority to EP 99106656.4, filedApr. 1, 1999.

The present invention relates to the isolation, identification andcharacterization of recombinant DNA molecules encoding enzymescatalysing the transfer of fatty acids from phospholipids todiacylglycerol in the biosynthetic pathway for the production oftriacylglycerol.

Triacylglycerol (TAG) is the most common lipid-based energy reserve innature. The main pathway for synthesis of TAG is believed to involvethree sequential acyl-transfers from acyl-CoA to a glycerol backbone (1,2). For many years, acyl-CoA:diacylglycerol acyltransferase (DAGAT),which catalyzes the third acyl transfer reaction, was thought to be theonly unique enzyme involved in TAG synthesis. It acts by divertingdiacylglycerol (DAG) from membrane lipid synthesis into TAG (2). Genesencoding this enzyme were recently identified both in the mouse (3) andin plants (4, 5), and the encoded proteins were shown to be homologousto acyl-CoA:cholesterol acyltransferase (ACAT). It was also recentlyreported that another DAGAT exists in the oleaginous fungus Mortierellaramanniana, which is unrelated to the mouse DAGAT, the ACAT gene familyor to any other known gene (6).

The instant invention relates to novel type of enzymes and theirencoding genes for transformation. More specifically, the inventionrelates to use of a type of genes encoding a not previously describedtype of enzymes hereinafter designated phospholipid:diacylglycerolacyltransferases (PDAT), whereby this enzyme catalyses anacyl-CoA-independent reaction. The said type of genes expressed alone intransgenic organisms will enhance the total amount of oil(triacylglycerols) produced in the cells. The PDAT genes, in combinationwith a gene for the synthesis of an uncommon fatty acid will, whenexpressed in transgenic organisms, enhance the levels of the uncommonfatty acids in the triacylglycerols.

There is considerable interest world-wide in producing chemicalfeedstock, such as fatty acids, for industrial use from renewable plantresources rather than non-renewable petrochemicals. This concept hasbroad appeal to manufacturers and consumers on the basis of resourceconservation and provides significant opportunity to develop newindustrial crops for agriculture.

There is a diverse array of unusual fatty acids in oils from wild plantspecies and these have been well characterised. Many of these acids haveindustrial potential and this had led to interest in domesticatingrelevant plant species to enable agricultural production of particularfatty acids.

Development in genetic engineering technologies combined with greaterunderstanding of the biosynthesis of unusual fatty acids now makes itpossible to transfer genes coding for key enzymes involved in thesynthesis of a particular fatty acid from a wild species intodomesticated oilseed crops. In this way individual fatty acids can beproduced in high purity and quantities at moderate costs.

In all crops like rape, sunflower, oilpalm etc., the oil (i.e.triacylglycerols) is the most valuable product of the seeds or fruitsand other compounds like starch, protein, and fibre is regarded asby-products with less value. Enhancing the quantity of oil per weightbasis at the expense of other compounds in oil crops would thereforeincrease the value of crop. If genes, regulating the allocation ofreduced carbon into the production of oil can be up-regulated, the cellswill accumulate more oil on the expense of other products. Such genesmight not only be used in already high oil producing cells such as oilcrops but could also induce significant oil production in moderate orlow oil containing crops such as e.g. soy, oat, maize, potato,sugarbeats, and turnips as well as microorganisms.

SUMMARY OF THE INVENTION

Many of the unusual fatty acids of interest, e.g. medium chain fattyacids, hydroxy fatty acids, epoxy fatty acids and acetylenic fattyacids, have physical properties that are distinctly different from thecommon plant fatty acids. The present inventors have found that, inplant species naturally accumulating these uncommon fatty acids in theirseed oil (i.e. triacylglycerol), these acids are absent, or present invery low amounts in the membrane (phospho)lipids of the seed. The lowconcentration of these acids in the membrane lipids is most likely aprerequisite for proper membrane function and thereby for proper cellfunctions. One aspect of the invention is that seeds of transgenic cropscan be made to accumulate high amounts of uncommon fatty acids if thesefatty acids are efficiently removed from the membrane lipids andchannelled into seed triacylglycerols.

The inventors have identified a novel class of enzymes in plantscatalysing the transfer of fatty acids from phospholipids todiacylglycerol in the production of triacylglycerol through anacyl-CoA-independent reaction and that these enzymes(phospholipid:diacylglycerol acyltransferases abbreviated as PDAT) areinvolved in the removal of hydroxylated, epoxygenated fatty acids, andprobably also other uncommon fatty acids such as medium chain fattyacids, from phospholipids in plants.

This enzyme reaction was shown to be present in microsomal preparationfrom baker's yeast (Saccharomyces cerevisiae). The instant inventionfurther pertains to an enzyme comprising an amino acid sequence as setforth in SEQ ID NO. 2 or a functional fragment, derivative, allele,homologous or isoenzyme thereof. A so called “knock out” yeast mutant,disrupted in the respective gene was obtained and microsomal membranesfrom the mutant was shown to totally lack PDAT activity. Thus, it wasproved that the disrupted gene encodes for a PDAT enzyme (SEQ ID NO. 1and 2).

Further genes and/or proteins of so far unknown function were identifiedand are contemplated within the scope of the instant invention. A genefrom Schizosaccharomyces pombe, SPBC776.14 (SEQ ID NO. 3), a putativeopen reading frame CAA22887 of the SPBC776.14 (SEQ ID NO. 13) wereidentified. Further Arabidopsis thaliana genomic sequences (SEQ ID NO.4, 10 and 11) coding for putative proteins were identified, as well as aputative open reading frame AAC80628 from the A. thaliana locus AC004557 (SEQ ID NO. 14) and a putative open reading frame AAD10668 fromthe A. thaliana locus AC 003027 (SEQ ID NO. 15) were identified.

Also, partially sequenced cDNA clone from Neurospora crassa (SEQ ID NO.9) and a Zea mays EST (Extended Sequence Tac) clone (SEQ ID NO. 7) andcorresponding putative amino acid sequence (SEQ ID NO. 8) wereidentified. Finally, two cDNA clones were identified, one Arabidopsisthaliana EST (SEQ ID NO. 5 and corresponding predicted amino acidsequence SEQ ID NO. 6) and a Lycopersicon esculentum EST clone (SEQ IDNO. 12) were identified. Further, enzymes designated as PDAT comprisingan amino acid sequence selected from the group consisting of sequencesas set forth in SEQ ID NO. 16, 17 and 18 are contemplated within thescope of the invention. Moreover, an enzyme comprising an amino acidsequence encoded through a nucleotide sequence, a portion, derivative,allele or homologue thereof selected from the group consisting ofsequences as set forth in SEQ ID NO. 1, 3, 4, 5, 7, 9, 10, 11, 12, 18 or19 or a functional fragment, derivative, allele, homologue or isoenzymeof the enzyme encoding amino acid sequence are included within the scopeof the invention.

A functional fragment of the instant enzyme is understood to be anypolypeptide sequence which shows specific enzyme activity of aphospholipid:diacylglycerol acyltransferase (PDAT). The length of thefunctional fragment can for example vary in a range from about 660±10amino acids to 660±250 amino acids, preferably from about 660±50 to660±100 amino acids, whereby the “basic number” of 660 amino acidscorresponds in this case to the polypeptide chain of the PDAT enzyme ofSEQ ID NO. 2 encoded by a nucleotide sequence according to SEQ ID NO. 1.Consequently, the “basic number” of functional full length enzyme canvary in correspondance to the encoding nucleotide sequence.

A portion of the instant nucleotide sequence is meant to be anynucleotide sequence encoding a polypeptide which shows specific activityof a phospholipid:diacylglycerol acyltransferase (PDAT). The length ofthe nucleotide portion can vary in a wide range of about severalhundreds of nucleotides based upon the coding region of the gene or ahighly conserved sequence. For example the length varies in a range formabout 1900±10 to 1900±1000 nucleotides, preferably form about 1900±50 to1900±700 and more preferably from about 1900±100 to 1900±500nucleotides, whereby the “basic number” of 1900 nucleotides correspondsin this case to the encoding nucleotide sequence of the PDAT enzyme ofSEQ ID NO. 1. Consequently, the “basic number” of functional full lengthgene can vary.

An allelic variant of the instant nucleotide sequence is understood tobe any different nucleotide sequence which encodes a polypeptide with afunctionally equivalent function. The alleles pertain naturallyoccurring variants of the instant nucleotide sequences as well assynthetic nucleotide sequences produces by methods known in the art.Contemplated are even altered nucleotide sequences which result in anenzyme with altered activity and/or regulation or which is resistantagainst specific inhibitors. The instant invention further includesnatural or synthetic mutations of the originally isolated nucleotidesequences. These mutations can be substitution, addition, deletion,inversion or insertion of one or more nucleotides.

A homologues nucleotide sequence is understood to be a complementarysequence and/or a sequence which specifically hybridizes with theinstant nucleotide sequence. Hybridizing sequences include similarsequences selected from the group of DNA or RNA which specificallyinteract to the instant nucleotide sequences under at least moderatestringency conditions which are known in the art. A preferred,non-limiting example of stringent hybridization conditions arehybridization in 6× sodium chloride/sodium citrate (SSC) at about 45°C., followed by one or more washes in 0.2×SSC, 0.1% SDS at 50-65° C.This further includes short nucleotide sequences of e.g. 10 to 30nucleotides, preferably 12 to 15 nucleotides. Included are also primeror hybridization probes.

A homologue nucleotide sequence included within the scope of the instantinvention is a sequence which is at least about 40%, preferably at leastabout 50% or 60%, and more preferably at least about 70%, 80% or 90% andmost preferably at least about 95%, 96%, 97%, 98% or 99% or morehomologous to a nucleotide sequence of SEQ ID NO. 1.

All of the aforementioned definitions are true for amino acid sequencesand functional enzymes and can easily transferred by a person skilled inthe art.

Isoenzymes are understood to be enzymes which have the same or a similarsubstrate specifity and/or catalytic activity but a different primarystructure.

In a first embodiment, this invention is directed to nucleic acidsequences that encode a PDAT. This includes sequences that encodebiologically active PDATs as well as sequences that are to be used asprobes, vectors for transformation or cloning intermediates. The PDATencoding sequence may encode a complete or partial sequence dependingupon the intended use. All or a portion of the genomic sequence, cDNAsequence, precursor PDAT or mature PDAT is intended.

Further included is a nucleotide sequence selected from the groupconsisting of sequences set forth in SEQ ID NO. 1, 3, 4, 10 or 11 or aportion, derivative, allele or homologue thereof. The invention pertainsa partial nucleotide sequence corresponding to a full length nucleotidesequence selected from the group consisting of sequences set forth inSEQ ID NO. 5, 7, 9, 12, 18 or 19 or a portion, derivative, allele orhomologue thereof. Moreover, a nucleotide sequence comprising anucleotide sequence which is at least 40% homologous to a nucleotidesequence selected from the group consisting of those sequences set forthin SEQ ID NO. 1, 3, 4, 5, 7, 9, 10, 11, 12, 18 or 19 is contemplatedwithin the scope of the invention.

The instant invention pertains to a gene construct comprising a saidnucleotide sequences of the instant invention which is operably linkedto a heterologous nucleic acid.

The term operably linked means a serial organisation e.g. of a promoter,coding sequence, terminator and/or further regulatory elements wherebyeach element can fulfill its original function during expression of thenucleotide sequence.

Further, a vector comprising of a said nucleotide sequence of theinstant invention is contemplated in the instant invention. Thisincludes also an expression vector as well as a vector furthercomprising a selectable marker gene and/or nucleotide sequences for thereplication in a host cell and/or the integration into the genome of thehost cell.

In a different aspect, this invention relates to a method for producinga PDAT in a host cell or progeny thereof, including geneticallyengineered oil seeds, yeast and moulds or any other oil accumulatingorganism, via the expression of a construct in the cell. Cellscontaining a PDAT as a result of the production of the PDAT encodingsequence are also contemplated within the scope of the invention.

Further, the invention pertains a transgenic cell or organism containinga said nucleotide sequence and/or a said gene construct and/or a saidvector. The object of the instant invention is further a transgenic cellor organism which is an eucaryotic cell or organism. Preferably, thetransgenic cell or organism is a yeast cell or a plant cell or a plant.The instant invention further pertains said transgenic cell or organismhaving an altered biosynthetic pathway for the production oftriacylglycerol. A transgenic cell or organism having an altered oilcontent is also contemplated within the scope of this invention.

Further, the invention pertains a transgenic cell or organism whereinthe activity of PDAT is altered in said cell or organism. This alteredactivity of PDAT is characterized by an alteration in gene expression,catalytic activity and/or regulation of activity of the enzyme.Moreover, a transgenic cell or organism is included in the instantinvention, wherein the altered biosynthetic pathway for the productionof triacylglycerol is characterized by the prevention of accumulation ofundesirable fatty acids in the membrane lipids.

In a different embodiment, this invention also relates to methods ofusing a DNA sequence encoding a PDAT for increasing the oil-contentwithin a cell.

Another aspect of the invention relates to the accommodation of highamounts of uncommon fatty acids in the triacylglycerol produced within acell, by introducing a DNA sequence producing a PDAT that specificallyremoves these fatty acids from the membrane lipids of the cell andchannel them into triacylglycerol. Plant cells having such amodification are also contemplated herein.

Further, the invention pertains a process for the production oftriacylglycerol, comprising growing a said transgenic cell or organismunder conditions whereby the said nucleotide sequence is expressed andwhereby the said transgenic cells comprising an said enzyme catalysingthe transfer of fatty acids from phospholipids to diacylglycerol formingtriacylglycerol.

Moreover, triacylglycerols produced by the aforementioned process areincluded in scope of the instant invention.

Object of the instant invention is further the use of an instantnucleotide sequence and/or a said enzyme for the production oftriacylglycerol and/or triacylglycerols with uncommon fatty acids. Theuse of a said instant nucleotide sequence and/or a said enzyme of theinstant invention for the transformation of any cell or organism inorder to be expressed in this cell or organism and result in an altered,preferably increased oil content of this cell or organism is alsocontemplated within the scope of the instant invention.

A PDAT of this invention includes any sequence of amino acids, such as aprotein, polypeptide or peptide fragment obtainable from amicroorganism, animal or plant source that demonstrates the ability tocatalyse the production of triacylglycerol from a phospholipid anddiacylglycerol under enzyme reactive conditions. By “enzyme reactiveconditions” is meant that any necessary conditions are available in anenvironment (e.g., such factors as temperature, pH, lack of inhibitingsubstances) which will permit the enzyme to function.

Other PDATs are obtainable from the specific sequences provided herein.Furthermore, it will be apparent that one can obtain natural andsynthetic PDATs, including modified amino acid sequences and startingmaterials for synthetic-protein modelling from the exemplified PDATs andfrom PDATs which are obtained through the use of such exemplifiedsequences. Modified amino acid sequences include sequences that havebeen mutated, truncated, increased and the like, whether such sequenceswere partially or wholly synthesised. Sequences that are actuallypurified from plant preparations or are identical or encode identicalproteins thereto, regardless of the method used to obtain the protein orsequence, are equally considered naturally derived.

Further, the nucleic acid probes (DNA and RNA) of the present inventioncan be used to screen and recover “homologous” or “related” PDATs from avariety of plant and microbial sources.

Further, it is also apparent that a person skilled in the art can, withthe information provided in this application, in any organism identify aPDAT activity, purify an enzyme with this activity and thereby identifya “non-homologues” nucleic acid sequence encoding such an enzyme.

The present invention can be essentially characterized by the followingaspects:

-   -   1. Use of a PDAT gene (genomic clone or cDNA) for        transformation.    -   2. Use of a DNA molecule according to item 1 wherein said DNA is        used for transformation of any organism in order to be expressed        in this organism and result in an active recombinant PDAT enzyme        in order to increase oil content of the organism.    -   3. Use of a DNA molecule of item 1 wherein said DNA is used for        transformation of any organism in order to prevent the        accumulation of undesirable fatty acids in the membrane lipids.    -   4. Use according to item 1, wherein said PDAT gene is used for        transforming transgenic oil accumulating organisms engineered to        produce any uncommon fatty acid which is harmful if present in        high amounts in membrane lipids, such as medium chain fatty        acids, hydroxylated fatty acids, epoxygenated fatty acids and        acetylenic fatty acids.    -   5. Use according to item 1, wherein said PDAT gene is used for        transforming organisms, and wherein said organisms are crossed        with other oil accumulating organisms engineered to produce any        uncommon fatty acid which is harmful if present in high amounts        in membrane lipids, comprising medium chain fatty acids,        hydroxylated fatty acids, epoxygenated fatty acids and        acetylenic fatty acids.    -   6. Use according to item 1, wherein the enzyme encoded by said        PDAT gene of cDNA is coding for a PDAT with distinct acyl        specificity.    -   7. Use according to item 1 wherein said PDAT encoding gene or        cDNA, is derived from Saccharomyces cereviseae, or contain        nucleotide sequences coding for an amino acid sequence 30% or        more identical to the amino acid sequence of PDAT as presented        in SEQ ID NO. 2.    -   8. Use according to item 1 wherein said PDAT encoding gene or        cDNA is derived from Saccharomyces cereviseae, or contain        nucleotide sequences coding for an amino acid sequence 40% or        more identical to the amino acid sequence of PDAT as presented        in SEQ ID NO. 2.    -   9. Use according to item 1 wherein said PDAT encoding gene or        cDNA is derived from Saccharomyces cereviseae, or contain        nucleotide sequences coding for an amino acid sequence 60% or        more identical to the amino acid sequence of PDAT as presented        in SEQ ID NO. 2.    -   10. Use according to item 1 wherein said PDAT encoding gene or        cDNA is derived from Saccharomyces cereviseae, or contain        nucleotide sequences coding for an amino acid sequence 80% or        more identical to the amino acid sequence of PDAT as presented        in SEQ ID NO.2.    -   11. Use according to item 1 wherein said PDAT encoding gene or        cDNA is derived from plants or contain nucleotide sequences        coding for an amino acid sequence 40% or more identical to the        amino acid sequence of PDAT from Arabidopsis thaliana or to the        protein encoded by the full length counterpart of the partial        Zea mays, Lycopericon esculentum, or Neurospora crassa cDNA        clones.    -   12. Transgenic oil accumulating organisms comprising, in their        genome, a PDAT gene transferred by recombinant DNA technology or        somatic hybridization.    -   13. Transgenic oil accumulating organisms according to item 12        comprising, in their genome, a PDAT gene having specificity for        substrates with a particular uncommon fatty acid and the gene        for said uncommon fatty acid.    -   14. Transgenic organisms according to item 12 or 13 which are        selected from the group consisting of fungi, plants and animals.    -   15. Transgenic organisms according to item 12 or 13 which are        selected from the group of agricultural plants.    -   16. Transgenic organisms according to item 12 or 13 which are        selected from the group of agricultural plants and where said        PDAT gene is expressed under the control of a storage organ        specific promotor.    -   17. Transgenic organisms according to item 12 or 13 which are        selected from the group of agricultural plants and where said        PDAT gene is expressed under the control of a seed promotor.    -   18. Oils from organisms according to item 12-17.    -   19. A method for altering acyl specificity of a PDAT by        alteration of the nucleotide sequence of a naturally occurring        encoding gene and as a consequence of this alternation creating        a gene encoding for an enzyme with novel acyl specifity.    -   20. A protein encoded by a DNA molecule according to item 1 or a        functional fragment thereof.    -   21. A protein of item 20 designated phospholipid:diacylglycerol        acyltransferase.    -   22. A protein of item 21 which has a distinct acyl specificity.    -   23. A protein of item 13 having the amino acid sequence as set        forth in SEQ ID NO. 2, 13, 14 or 15 (and the proteins encoded by        the full length or partial genes set forth in SEQ. ID. NO. 1, 3,        4, 5, 7, 9, 10, 11 or 12) or an amino acid sequence with at        least 30% homology to said amino acid sequence.    -   24. A protein of item 23 isolated from Saccharomyces cereviseae.

DESCRIPTION OF FIGURES

FIG. 1:

Metabolism of ¹⁴C-labeled PC into the neutral lipid fraction by plantmicrosomes. (A) Microsomes from developing seeds of sunflower, R.communis and C. palaestina were incubated for 80 mi at 30° C. with PC (8nmol) having oleic acid in its sn-1 position, and either ¹⁴C-labeledoleic, ricinoleic or vernolic acid in its sn-2 position. Radioactivityincorporated in TAG (open bars), DAG (solid bars), and unsterified fattyacids (hatched bars) was quantified using thin layer chromatographyfollowed by electronic autoradiography, and is shown as percentage ofadded labeled substrate. (B) Synthesis in vitro of TAG carrying twovernoloyl and one [¹⁴C] ricinoleoyl group by microsomes from R.communis. The substrates added were unlabeled divernoloyl-DAG (5 nmol),together with either sn-1-oleoyl-sn-2-[¹⁴C] ricinoleoyl-DAG (0.4 nmol,770 dpm/nmol) or sn-1-oleoyl-sn-2-[¹⁴C] ricinoleoyl-PC (0.4 nmol, 7700dpm/nmol). The microsomes were incubated with the substrates for 30 minat 30° C., after which samples were removed for lipid analysis asdescribed in the section “general methods”. The data shown are theaverage of two experiments.

FIG. 2:

PDAT activity in yeast microsomes, as visualized by autoradiogram ofneutral lipid products separated on TLC. Microsomal membranes (10 nmolof PC) from the wild type yeast strain FY1679 (lanes 1-3), a congenicyeast strain (FVKT004-04C(AL)) that is disrupted for YNR008w (lane 4) orthe same disruption strain transformed with the plasmid pUS1, containingthe YNR008w gene behind its native promoter (lane 5), were assayed forPDAT activity. As substrates, we used 2 nmol sn-1-oleoyl-sn-2-[¹⁴C]ricinoleoyl-PC together with either 5 nmol of dioleoyl-DAG (lanes 2, 4and 5) or rac-oleoyl-vernoleoyl-DAG (lane 3). The enzymatic assay andlipid analysis was performed as described in Materials and Methods. Thecells were precultured for 20 h in liquid YPD medium, harvested andre-suspended in an equal volume of minimal medium (19) containing 16 g/lglycerol. The cells were then grown for an additional 24 h prior tobeing harvested. Selection for the plasmid was maintained by growing thetransformed cells in synthetic medium lacking uracil (18).Abbreviations: 1-OH-TAG, monoricinoleoyl-TAG; 1-OH-1-ep-TAG,monoricinoleoyl-monovernoloyl-TAG; OH-FA, unesterified ricinoleic acid.

FIG. 3:

Lipid content (A, B) and PDAT activity (C) in PDAT overexpressing yeastcells. The PDAT gene in the plasmid pUS4 was overexpressed from thegalactose-induced GAL1-TPK2 promoter in the wild type strain W303-1A(7). Its expression was induced after (A) 2 hours or (B) 25 hours ofgrowth by the addition of 2% final concentration (w/v) of galactose. Thecells were then incubated for another 22 hours before being harvested.The amount of lipids of the harvested cells was determined byGLC-analysis of its fatty acid contents and is presented as μmol fattyacids per mg dry weight in either TAG (open bar), polar lipids (hatchedbar), sterol esters (solid bar) and other lipids (striped bar). The datashown are the mean values of results with three independent yeastcultures. (C) In vitro synthesis of TAG by microsomes prepared fromyeast cells containing either the empty vector (vector) or the PDATplasmid (+PDAT). The cells were grown as in FIG. 3A. The substratelipids dioleoyl-DAG (2.5 nmol) and sn-1-oleoyl-sn-2-[¹⁴C] ricinoleoyl-PC(2 nmol) were added to aliquots of microsomes (10 nmol PC), which werethen incubated for 10 min at 28° C. The amount of label incorporatedinto TAG was quantified by electronic autoradiography. The results shownare the mean values of to experiments.

FIG. 4:

Substrate specificity of yeast PDAT. The PDAT activity was assayed byincubating aliquots of lyophilized microsomes (10 nmol PC) withsubstrate lipids at 30° C. for 10 min (panel A) or 90 min (panel B).Unlabeled DAG (2.5 nmol) was used as substrates together with differentlabeled phospholipids, as shown in the figure. (A) Sn-positionspecificity of yeast PDAT regarding the acyl donor substrate.Dioleoyl-DAG together with either sn-1-[¹⁴C] oleoyl-sn-2-[¹⁴C]oleoyl-PC(di-[¹⁴C]-PC), sn-1-[¹⁴C] oleoyl-sn-2-oleoyl-PC (sn-1-[¹⁴C]-PC) orsn-1-oleoyl-sn-2-[¹⁴C]oleoyl-PC (sn-2-[¹⁴C]-PC). (B) Specificity ofyeast PDAT regarding phospholipid headgroup and of the acyl compositionof the phospholipid as well as of the diacylglycerol. Dioleoyl-DAGtogether with either sn-1-oleoyl-sn-2-[¹⁴C]oleoyl-PC (oleoyl-PC),sn-1-oleoyl-sn-2-[¹⁴C]oleoyl-PE (oleoyl-PE), sn-1-oleoyl-sn-2-[¹⁴C]ricinoleoyl-PC (ricinoleoyl-PC) or sn-1-oleoyl-sn-2-[¹⁴C] vernoloyl-PC(vernoloyl-PC). In the experiments presented in the 2 bars to the farright, monoricinoleoyl-DAG (ricinoleoyl-DAG or mono-vernoloyl-DAG(vernoloyl-DAG) were used together with sn-1-oleoyl-sn-2-[¹⁴C]oleoyl-PC.The labeled that was incorporated into TAG (solid bars) and lyso-PC(LPC, open bars) was quantified by electronic autoradiography. Theresults shown are the mean values of two experiments. The microsomesused were from W303-1A cells overexpressing the PDAT gene from theGAL1-TPK2 promoter, as described in FIG. 3. The expression was inducedat early stationary phase and the cells were harvested after anadditional 24 h.

TAB. 1:

In vitro synthesis of triacylglycerols in microsomal preparations ofdeveloping castor bean. Aliquots of microsomes (20 nmol PC) werelyophilised and substrate lipids were added in benzene solution: (A) 0.4nmol [¹⁴C]-DAG (7760 dpm/nmol) and where indicated 1.6 nmol unlabeledDAG; (B) 0.4 nmol [¹⁴C]-DAG (7760 dpm/nmol) and 5 nmol unlabeleddi-ricinoleoyl-PC and (C) 0.25 nmol [¹⁴C]-PC (4000 dpm/nmol) and 5 nmolunlabeled DAG. The benzene was evaporated by N₂ and 0.1 ml of 50 mMpotassium phosphate was added, thoroughly mixed and incubated at 30° C.for (A) 20 min.; (B) and (C) 30 min. Assays were terminated byextraction of the lipids in chloroform. The lipids were then separatedby thin layer chromatography on silica gel 60 plates (Merck; Darmstadt,Germany) in hexan/diethlether/acetic 35:70:1.5. The radioactive lipidswere visualized and the radioactivity quantified on the plate byelectronic autoradiography (Instant Imager, Packard, U.S.). Results arepresented as mean values of two experiments.

Radioactivity in different triacylglycerols (TAG) species formed.Abbreviations used: 1-OH—, mono-ricinoleoyl-; 2-OH, di-ricinoleoyl-;3-OH—, triricinoleoyl; 1-OH-1-ver-, mono-ricinoleoyl-monovernoleoyl-;1-OH-2-ver-, mono-ricinoleoyl-divernoleoyl-. Radiolabeled DAG and PCwere prepared enzymatically. The radiolabeled ricinoleoyl group isattached at the sn-2-position of the lipid and unlabeled oleoyl group atthe sn-1-position. Unlabeled DAG with vernoleoyl -or ricinoleoyl chainswere prepared by the action of TAG lipase (6) on oil of Euphorbialagascae or Castor bean, respectively. Synthetic di-ricinoleoyl-PC waskindly provided from Metapontum Agribios (Italy).

TAB. 2:

Total fatty acids per mg of T2 seeds pooled from individual Arabidopsisthaliana plants transformed with yeast PDAT gene under the control ofnapin promoter (26-14) or transformed with empty vector (32-4).

-   -   *=statistical difference between control plants and PDAT        transformed plants in a mean different two-sided test at α=5.

DESCRIPTION OF THE SEQ ID:

SEQ ID NO. 1: Genomic DNA sequence and suggested amino acid sequence ofthe Saccharomyces cerevisiae PDAT gene, YNR008w, with GenBank accessionnumber Z71623 and Y13139, and with nucleotide ID number 1302481.

SEQ ID NO. 2: The amino acid sequence of the suggested open readingframe YNR008m from Saccharomyces cerevisiae.

SEQ ID NO. 3: Genomic DNA sequence of the Schizosaccharomyces pombegeneSPBC776.14.

SEQ ID NO. 4: Genomic DNA sequence of part of the Arabidopsis thalianalocus with GenBank accession number AB006704.

SEQ ID NO. 5: Nucleotide sequence of the Arabidopsis thaliana cDNA clonewith GenBank accession number T04806, and nucleotide ID number 315966.

SEQ ID NO. 6: Predicted amino acid sequence of the Arabidopsis thalianacDNA clone with GenBank accession number T04806.

SEQ ID NO. 7: Nucleotide and amino acid sequence of the Zea mays ESTclone with GenBank accession number AI461339, and nucleotide ID numberg4288167.

SEQ ID NO. 8: Predicted amino acid sequence of the Zea mays EST clonewith GenBank accession number AI461339, and nucleotide ID numberg4288167.

SEQ ID NO. 9: DNA sequence of part of the Neurospora crassa EST cloneW07G1, with GenBank accession number AI398644, and nucleotide ID numberg4241729.

SEQ ID NO. 10: Genomic DNA sequence of part of the Arabidopsis thalianalocus with GenBank accession number AC004557.

SEQ ID NO. 11: Genomic DNA sequence of part of the Arabidopsis thalianalocus with GenBank accession number AC003027.

SEQ ID NO. 12: DNA sequence of part of the Lycopersicon esculentum cDNAclone with GenBank accession number AI486635.

SEQ ID NO. 13: Amino acid sequence of the Schizosaccharomyces pombeputative opening reading frame CAA22887 of the Schizosaccharomyces pombegene SPBC776.14.

SEQ ID NO. 14: Amino acid sequence of the Arabidopsis thaliana putativeopen reading frame AAC80628 derived from the Arabidopsis thaliana locuswith GenBank accession number AC004557.

SEQ ID NO. 15: Amino acid sequence of the Arabidopsis thaliana putativeopen reading frame AAD10668 derived from the Arabidopsis thaliana locuswith GenBank accession number AC003027.

SEQ ID NO. 16: Amino acid sequence of the region of the Arabidopsisthaliana genomic sequence (AC004557).

SEQ ID NO. 17: Amino acid sequence of the region of the Arabidopsisthaliana genomic sequence (AB006704).

SEQ ID NO. 20: The amino acid sequence of the yeast ORF YNR008w sequenceand amino acid sequence of the yeast ORF YNR008w from Saccharomycescerevisiae derived from the corresponding genomic DNA sequence.

SEQ ID NO. 18: Nucleotide sequence and the corresponding amino acidsequence of the Arabidopsis thaliana EST-clone with GenBank accessionnumber T04806, and ID number 315966.

SEQ ID NO. 19: DNA sequence of part of the Neurospora crassa cDNA cloneWO7G1, ID number g4241729.

DETAILED DESCRIPTION OF THE INVENTION

General Methods

Yeast strains and plasmids. The wild type yeast strains used were eitherFY1679 (MATα his3-Δ200 leu2-Δ1 trp1-Δ6 ura3-52) or W303-1A (MATa ADE2-1can1-100 his3-11,15 leu2-3,112 trp1-1 ura3-1) (7). The YNR008w::KanMX2disruption strain FVKT004-04C(AL), which is congenic to FY1679, wasobtained from the Euroscarf collection (8). A 2751 bp fragmentcontaining the YNR008w gene with 583 bp of 5′ and 183 bp of 3′ flankingDNA was amplified from W303-1A genomic DNA using Taq polymerase with5′-TCTCCATCTTCTGCAAAACCT-3′ and 5′-CCTGTCAAAAACCTTCTCCTC-3′ as primers.The resulting PCR product was purified by agarose gel electrophoresisand cloned into the EcoRV site of pBluescript (pbluescript-pdat). Forcomplementation experiments, the cloned fragment was released frompBluescript by HindIII-SacI digestion and then cloned between theHindIII and SacI sites of pFL39 (9), thus generating pUS1. Foroverexpression of the PDAT gene, a 2202 bp EcoRI fragment from thepBluescript plasmid which contains only 24 bp of 5′ flanking DNA wascloned into the BamHI site of the GAL1-TPK2 expression vector pJN92(12), thus generating pUS4.

Microsomal preparations. Microsomes from developing seeds of sunflower(Helianthus annuus), Ricinus communis and Crepis palaestina wereprepared using the procedure of Stobart and Stymne (11). To obtain yeastmicrosomes, 1 g of yeast cells (fresh weight) was re-suspended in 8 mlof ice-cold buffer (20 mM Tris-Cl, pH 7.9, 10 mM MgCl₂, 1 mM EDTA, 5%(v/v) glycerol, 1 mM DTT, 0.3 M ammonium sulfate) in a 12 ml glass tube.To this tube, 4 ml of glass beads (diameter 0.45-0.5 mm) were added, andthe tube was then heavily shaken (3×60 s) in an MSK cell homogenizer (B.Braun Melsungen AG, Germany). The homogenized suspension was centrifugedat 20,000×g for 15 min at 6° C. and the resulting supernatant was againcentrifuged at 100,000×g for 2 h at 6° C. The 100,000×g pellet wasresuspended in 0.1 M potassium phosphate (pH 7.2), and stored at −80° C.It is subsequently referred to as the crude yeast microsomal fraction.

Lipid substrates. Radio-labeled ricinoleic (12-hydroxy-octadecenoic) andvernolic (12,13-epoxy-octadecenoic) acids were synthesized enzymaticallyfrom [1-¹⁴C]oleic acid and [1-¹⁴C]linoleic acid, respectively, byincubation with microsomal preparations from seeds of Ricinus communisand Crepis palaestina, respectively (12). The synthesis ofphosphatidylcholines (PC) or phosphatidylethanolamines (PE) with¹⁴C-labeled acyl groups in the sn-2 position was performed using eitherenzymatic (13), or synthetic (14) acylation of [¹⁴C]oleic,[¹⁴C]ricinoleic, or [¹⁴C]vernolic acid. Dioleoyl-PC that was labeled inthe sn-1 position was synthesized from sn-1-[¹⁴C]oleoyl-lyso-PC andunlabeled oleic acid as described in (14).Sn-1-oleoyl-sn-2-[¹⁴C]ricinoleoyl-DAG was synthesized from PC by theaction of phospholipase C type XI from B. Cereus (Sigma Chemical Co.) asdescribed in (15). Monovernoloyl- and divernoleoyl-DAG were synthesizedfrom TAG extracted from seeds of Euphorbia lagascae, using theTAG-lipase (Rizhopus arrhizus, Sigma Chemical Co.) as previouslydescribed (16). Monoricinoleoyl-TAG was synthesized according to thesame method using TAG extracted from Castor bean.

Lipid analysis. Total lipid composition of yeast were determined fromcells harvested from a 40 ml liquid culture, broken in a glass-beadshaker and extracted into chloroform as described by Bligh and Dyer(17), and then separated by thin layer chromatography inhexane/diethylether/acetic acid (80:20:1) using pre-coated silica gel 60plates (Merck). The lipid areas were located by brief exposure to I₂vapors and identified by means of appropriate standards. Polar lipids,sterol-esters and triacylglycerols, as well as the remaining minor lipidclasses, referred to as other lipids, were excised from the plates.Fatty acid methylesters were prepared by heating the dry excisedmaterial at 85° C. for 60 min in 2% (v/v) sulfuric acid in dry methanol.The methyl esters were extracted with hexane and analyzed by GLC througha 50 m×0.32 mm CP-Wax58-CB fused-silica column (Chrompack), withmethylheptadecanoic acid as an internal standard. The fatty acid contentof each fraction was quantified and used to calculate the relativeamount of each lipid class. In order to determine the total lipidcontent, 3 ml aliquots from yeast cultures were harvested bycentrifugation and the resulting pellets were washed with distilledwater and lyophilized. The weight of the dried cells was determined andthe fatty acid content was quantified by GLC-analyses after conversionto methylesters as described above. The lipid content was thencalculated as nmol fatty acid (FA) per mg dry weight yeast.

Enzyme assays. Aliquots of crude microsomal fractions (corresponding to10 nmol of microsomal PC) from developing plant seeds or yeast cellswere lyophilized over night. ¹⁴C-Labeled substrate lipids dissolved inbenzene were then added to the dried microsomes. The benzene wasevaporated under a stream of N₂, leaving the lipids in direct contactwith the membranes, and 0.1 ml of 50 mM potassium phosphate (pH 7.2) wasadded. The suspension was thoroughly mixed and incubated at 30° C. forthe time period indicated, up to 90 min. Lipids were extracted from thereaction mixture using chloroform and separated by thin layerchromatography in hexane/diethylether/acetic acid (35:70:1.5) usingsilica gel 60 plates (Merck). The radioactive lipids were visualized andquantified on the plates by electronic autoradiography (Instant Imager,Packard, US).

Yeast cultivation. Yeast cells were grown at 28° C. on a rotatory shakerin liquid YPD medium (1% yeast extract, 2% peptone, 2% glucose),synthetic medium (18) containing 2% (v/v) glycerol and 2% (v/v) ethanol,or minimal medium (19) containing 16 g/l of glycerol.

The instant invention is further characterized by the following exampleswhich are not limiting:

Acyl-CoA-independent synthesis of TAG by oil seed microsomes. A largenumber of unusual fatty acids can be found in oil seeds (20). Many ofthese fatty acids, such as ricinoleic (21) and vernolic acids (22), aresynthesized using phosphatidylcholin (PC) with oleoyl or linoleoylgroups esterified to the sn-2 position, respectively, as the immediateprecursor. However, even though PC can be a substrate for unusual fattyacid synthesis and is the major membrane lipids in seeds, unusuallyfatty acids are rarely found in the membranes. Instead, they are mainlyincorporated into the TAG. A mechanism for efficient and selectivetransfer of these unusual acyl groups from PC into TAG must thereforeexist in oil seeds that accumulate such unusual fatty acids. Thistransfer reaction was biochemically characterized in seeds from castorbean (Ricinus communis) and Crepis palaestina, plants which accumulatehigh levels of ricinoleic and vernolic acid, respectively, and sunflower(Helianthus annuus), a plant which has only common fatty acids in itsseed oil. Crude microsomal fractions from developing seeds wereincubated with PC having ¹⁴C-labeled oleoyl, ricinoleoyl or vernoloylgroups at the sn-2 position. After the incubation, lipids were extractedand analyzed by thin layer chromatography. We found that the amount ofradioactivity that was incorporated into the neutral lipid fractionincreased linearly over a period of 4 hours (data not shown). Thedistribution of [¹⁴C]acyl groups within the neutral lipid fraction wasanalyzed after 80 min (FIG. 1). Interestingly the amount anddistribution of radioactivity between different neutral lipids werestrongly dependent both on the plant species and on the type of[¹⁴C]acyl chain. Thus, sunflower microsomes incorporated most of thelabel into DAG, regardless of the type of [¹⁴C]acyl group. In contrast,R. communis microsomes preferentially incorporated [¹⁴C]ricinoleoyl and[¹⁴C]vernoloyl groups into TAG, while [¹⁴C]oleyl groups mostly werefound in DAG. C. palaestina microsomes, finally, incorporated only[¹⁴C]vernolyol groups into TAG, with [¹⁴C]ricinoleyl groups being foundmostly as free fatty acids, and [¹⁴C]oleyl groups in DAG. This showsthat the high in vivo levels of ricinoleic acid and vernolic acid in theTAG pool of R. communis and C. palaestina, respectively, can beexplained by an efficient and selective transfer of the correspondingacyl groups from PC to TAG in these organisms. The in-vitro synthesis oftriacylglycerols in microsomal preparations of developing castor bean issummarized in table 1.

PDAT: a novel enzyme that catalyzes acyl-CoA-independent synthesis ofTAG. It was investigated if DAG could serve both as an acyl donor aswell as an acyl acceptor in the reactions catalyzed by the oil seedmicrosomes. Therefore, unlabeled divernoloyl-DAG was incubated witheither sn-1-oleoyl-sn-2-[¹⁴C]ricinoleoyl-DAG orsn-1-oleoyl-sn-2-[¹⁴C]ricinoleoyl-PC in the presence of R. communismicrosomes. The synthesis of TAG molecules containing both[¹⁴C]ricinoleoyl and vernoloyl groups was 5 fold higher when[¹⁴C]ricinoleoyl-PC served as acyl donor as compared to[¹⁴C]ricinoleoyl-DAG (FIG. 1B). These data strongly suggests that PC isthe immediate acyl donor and DAG the acyl acceptor in theacyl-CoA-independent formation of TAG by oil seed microsomes. Therefore,this reaction is catalyzed by a new enzyme which we calledphospholipid:diacylglycerol acyltransferase (PDAT).

PDAT activity in yeast microsomes. Wild type yeast cells were cultivatedunder conditions where TAG synthesis is induced. Microsomal membraneswere prepared from these cells and incubated withsn-2-[¹⁴C]-ricinoleoyl-PC and DAG and the ¹⁴C-labeled products formedwere analyzed. The PC-derived [¹⁴C]ricinoleoyl groups within the neutrallipid fraction mainly were found in free fatty acids or TAG, and alsothat the amount of TAG synthesized was dependent on the amount of DAGthat was added to the reaction (FIG. 2). The in vitro synthesis of TAGcontaining both ricinoleoyl and vernoloyl groups, a TAG species notpresent in vivo, from exogenous added sn-2-[¹⁴C]ricinoleoyl-PC andunlabeled vernoloyl-DAG (FIG. 2, lane 3) clearly demonstrates theexistence of an acyl-CoA-independent synthesis of TAG involving PC andDAG as substrates in yeast microsomal membranes. Consequently, TAGsynthesis in yeast can be catalyzed by an enzyme similar to the PDATfound in plants.

The PDAT encoding gene in yeast. A gene in the yeast genome (YNR008w) isknown, but nothing is known about the function of YNR008w, except thatthe gene is not essential for growth under normal circumstances.Microsomal membranes were prepared from the yeast strain FVKT004-04C(AL)(8) in which the gene with unknown function had been disrupted. PDATactivity in the microsomes were assayed using PC with radiolabelledfatty acids at the sn-2 position. The activity was found to becompletely absent in the disruption strain (FIG. 2 lane 4).Significantly, the activity could be partially restored by the presenceof YNR008w on the single copy plasmid pUS1 (FIG. 2 lane 5). Moreover,acyl groups of phosphatidylethanolamine (PE) were efficientlyincorporated into TAG by microsomes from the wild type strain whereas noincorporation occurred from this substrate in the mutant strain. Thisshows that YNR008w encodes a yeast PDAT which catalyzes the transfer ofan acyl group from the sn-2 position of phospholipids to DAG, thusforming TAG. It should be noted that no cholesterol esters were formedfrom radioactive PC even in incubations with added ergosterols, nor werethe amount of radioactive free fatty acids formed from PC affected bydisruption of the YNR008w gene. This demonstrates that yeast PDAT do nothave cholesterol ester synthesising or phospholipase activities.

Increased TAG content in yeast cells that overexpress PDAT. The effectof overexpressing the PDAT-encoding gene was studied by transforming awild type yeast strain with the pUS4 plasmid in which the gene isexpressed from the galactose-induced GAL1:TPK2 promoter. Cellscontaining the empty expression vector were used as a control. The cellswere grown in synthetic glycerol-ethanol medium, and expression of thegene was induced after either 2 hours (early log phase) or 25 hours(stationary phase) by the addition of galactose. The cells were thenincubated for another 21 hours, after which they were harvested andassays were performed. We found that overexpression of PDAT had nosignificant effect on the growth rate as determined by the opticaldensity. However, the total lipid content, measured as total μmol fattyacids per mg yeast dry weight, was 47% (log phase) or 29% (stationaryphase) higher in the PDAT overexpressing strain than in the control.Furthermore, the polar lipid and sterolester content was unaffected byoverexpression of PDAT. Instead, the elevated lipid content in thesecells is entirely due to an increased TAG content (FIG. 3A,B). Thus, theamount of TAG was increased by 2-fold in PDAT overexpressing early logphase cells and by 40% in stationary phase cells. It is interesting tonote that a significant increase in the TAG content was achieved byoverexpressing PDAT even under conditions (i.e. in stationary phase)where DAGAT is induced and thus contributes significantly to TAGsynthesis. In vitro PDAT activity assayed in microsomes from the PDAToverexpressing strain was 7-fold higher than in the control strain, afinding which is consistent with the increased levels of TAG that weobserved in vivo (FIG. 3C). These results clearly demonstrate thepotential use of the PDAT gene in increasing the oil content intransgenic organisms.

Substrate specificity of yeast PDAT. The substrate specificity of yeastPDAT was analyzed using microsomes prepared from the PDAT overexpressingstrain (see FIG. 4). The rate of TAG synthesis, under conditions givenin FIG. 4 with di-oleoyl-PC as the acyl-donor, was 0.15 nmol per min andmg protein. With both oleoyl groups of PC labeled it was possible, underthe given assay conditions, to detect the transfer of 11 pmol/min of[¹⁴C]oleoyl chain into TAG and the formation of 15 pmol/min of lyso-PC.In microsomes from the PDAT-deficient strain, no TAG at all and onlytrace amounts of lyso-PC was detected, strongly suggesting that yeastPDAT catalyses the formation of equilmolar amounts of TAG and lyso-PCwhen supplied with PC and DAG as substrates. The fact that somewhat morelyso-PC than TAG is formed can be explained by the presence of aphospholipase in yeast microsomes, which produces lyso-PC andunesterified fatty acids from PC (data not shown).

The specificity of yeast PDAT for different acyl group positions wasinvestigated by incubating the microsomes with di-oleoyl-PC carrying a[¹⁴C]acyl group either at the sn-1 position (FIG. 4A bar 2) or the sn-2position (FIG. 4A bar 3). We found that the major ¹⁴C-labeled productformed in the former case was lyso-PC, and in the latter case TAG. Weconclude that yeast PDAT has a specificity for the transfer of acylgroups from the sn-2 position of the phospholipid to DAG, thus formingsn-1-lyso-PC and TAG. Under the given assay conditions, trace amounts of¹⁴C-labelled DAG is formed from the sn-1 labeled PC by the reversibleaction of a CDP-choline:choline phosphotransferase (data not shown).This labeled DAG can then be further converted into TAG by the PDATactivity. It is therefore not possible to distinguish whether the minoramounts of labeled TAG that is formed in the presence of di-oleoyl-PCcarrying a [¹⁴C]acyl group in the sn-1 position, is synthesized directlyfrom the sn-1-labeled PC by a PDAT that also can act on the sn-1position, or if it is first converted to sn-1-labeled DAG and thenacylated by a PDAT with strict selectivity for the transfer of acylgroups at the sn-2 position of PC. Taken together, this shows that thePDAT encoded by YNR008w catalyses an acyl transfer from the sn-2position of PC to DAG, thus causing the formation of TAG and lyso-PC.

The substrate specificity of yeast PDAT was further analyzed withrespect to the headgroup of the acyl donor, the acyl group transferredand the acyl chains of the acceptor DAG molecule. The two major membranelipids of S. cerevisiae are PC and PE, and as shown in FIG. 4B (bars 1and 2), dioleoyl-PE is nearly 4-fold more efficient than dioleoyl-PC asacyl donor in the PDAT-catalyzed reaction. Moreover, the rate of acyltransfer is strongly dependent on the type of acyl group that istransferred. Thus, a ricinoleoyl group at the sn-2 position of PC is 2.5times more efficiently transferred into TAG than an oleoyl group in thesame position (FIG. 4B bars 1 and 3). In contrast, yeast PDAT has nopreference for the transfer of vernoloyl groups over oleoyl groups (FIG.4B bars 1 and 4). The acyl chain of the acceptor DAG molecule alsoaffects the efficiency of the reaction. Thus, DAG with a ricinoleoyl ora vernoloyl group is a more efficient acyl acceptor than dioleoyl-DAG(FIG. 4B bars 1, 5 and 6). Taken together, these results clearly showthat the efficiency of the PDAT-catalyzed acyl transfer is stronglydependent on the properties of the substrate lipids.

PDAT genes. Nucleotide and amino acid sequences of several PDAT genesare given as SEQ ID NO. 1 through 15. Further provisional and/or partialsequences are given as SEQ ID NO. 16 through 19, respectively. One ofthe Arabidopsis genomic sequences (SEQ ID NO. 4) identified anArabidopsis EST cDNA clone; T04806. This cDNA clone was fullycharacterized and the nucleotide sequence is given as SEQ ID NO. 5.Based on the sequence homology of the T04806 cDNA and the Arabidopsisthaliana genomic DNA sequence (SEQ ID NO. 4) it is apparent that anadditional A is present at position 417 in the cDNA clone (data notshown). Excluding this nucleotide would give the amino acid representedby the nucleotide sequence depicted in SEQ ID NO. 12.

Increased TAG content in seeds of Arabidopsis thaliana that express theyeast PDAT. For the expression of the yeast pdat gene in Arabidopsisthaliana an EcoRI fragment from the pBluescript-pdat was cloned togetherwith napin promoter (26) into the vector pGPTV-KAN (27). A plasmid(pGNapPDAT) having the yeast PDAT gene in the correct orientation wasidentified and transformed into Agrobacterium tumefaciens. Thesebacteria were used to transform Arabidopsis thaliana columbia (C-24)plants using the root transformation method (28). Plants transformedwith an empty vector were used as controls.

First generation seeds (T1) were harvested and germinated on kanamycincontaining medium. Second generation seeds (T2) were pooled fromindividual plants and their fatty acid contents analysed byquantification of their methyl esthers by gas liquid chromatographyafter methylation of the seeds with 2% sulphuric acid in methanol at 85°C. for 1.5 hours. Quantification was done with heptadecanoic acid methylesters as internal standard.

From the transformation with pGNapPDAT one T1 plant (26-14) gave raiseto seven T2 plants of which 3 plants yielded seeds with statistically(in a mean difference two-sided test) higher oil content than seeds fromT2 plants generated from T1 plant 32-4 transformed with an empty vector(table 2).

References cited in the description:

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1. A process for the production of triacylglycerol, comprising: growinga transgenic plant cell or a yeast cell, a fungi, or a plant containing(i) the nucleotide sequence of SEQ ID NO: 1 from Saccharomycescerevisiae, or (ii) the nucleotide sequence that is 95% identical tosaid SEQ ID NO:1, wherein the nucleotide sequence of (i) and (ii) encodean enzyme (SEQ ID NO:2) that catalyzes in an acyl-CoA-independentreaction the transfer of fatty acids from phospholipids todiacylglycerol in the biosynthetic pathway for the production oftriacylglycerol.
 2. A method of producing triacylglycerol ortriacylglycerols with uncommon fatty acids comprising: transforming aplant cell or a yeast cell, a fungi, or a plant which produces uncommonfatty acids with (i) the nucleotide sequence of SEQ ID NO: 1 fromSaccharomyces cerevisiae, or (ii) the nucleotide sequence that is 95%identical to said SEQ ID NO: 1, wherein  the nucleotide sequence of (i)and (ii) encode SEQ ID NO: 2 whereby transformation results in theproduction of an enzyme (SEQ ID NO: 2) that catalyzes in anacyl-CoA-independent reaction the transfer of fatty acids fromphospholipids to diacylglycerol in the biosynthesis pathway for theproduction of triacylglycerol or triacylglycerols with uncommon fattyacids.
 3. A method of producing triacylglycerol or triacylglycerols forincreasing the oil content of an organism or cell comprising:transfecting a plant cell or a yeast cell, a fungi, or a plant with (i)the nucleotide of sequence of SEQ ID NO: 1 from Saccharomycescerevisiae, or (ii) the nucleotide sequence 95% identical to said SEQ IDNO: 1,  wherein the nucleotide sequence of (i) and (ii) encodes SEQ IDNO: 2 whereby transfection results in the production of an enzyme (SEQID NO: 2) that catalyzes in an acyl-CoA-independent reaction thetransfer of fatty acids from phospholipids to diacylglycerol in thebiosynthesis pathway for the production of triacylglycerol ortriacylglycerols thereby increasing the oil content of the plant cell orthe yeast cell, the fungi, or the plant.
 4. The method of claim 3wherein the oil content is increased in seeds.
 5. The process of claim 1wherein the process comprises the step of growing a transgenic plant oryeast cell, or plant.
 6. The method of claim 2 wherein the methodcomprises the step of transforming a transgenic plant or yeast cell, orplant.
 7. The method of claim 3 wherein the method comprises the step oftransfecting a transgenic plant or yeast cell, or plant.
 8. The methodof claim 2 wherein the uncommon fatty acids are in the form ofphospholipids.